Optical feedback stabilizing circuit for a voltage source having a high internal resistance



April 18, DEELMAN L OPTICAL FEEDBACK STABILIZING CIRCUIT FOR A VOLTAGE SOURCE HAVING A HIGH INTERNAL RESISTANCE Filed 001,- ll, 1965 rdus J.Deelman Gera Alphog sus M.H.Schcllekens 6'. 5 INVENTRS United States Patent 3,315,078 OPTICAL FEEDBACK STABILIZING CIRCUIT FUR A VOLTAGE SOURCE HAVING A HIGH INTER- NAL RESISTANCE Gerardus Jacobus Deeiman and Alphonsus Maria Henricus Schellekens, both of Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Oct. 11, 1963, Ser. No. 315,606 Claims priority, application Germany, Oct. 13, 1962, N 22,208 12 Claims. (Cl. 250-205) This invention relates to voltage regulators and more particularly to a regulator circuit for regulating the voltage from a voltage source of high internal impedance to a load by means of photosensitive elements.

With such a circuit-arrangement it is difficult to keep the voltage across the load constant in the case of a varying load. This problem is particularly conspicuous in the case where energy must be supplied to a display tube in a television receiver. If, because of a variation in the input signal the current passing through the tube varies, it is necessary to keep the voltage of the tube as constant as possible in order to avoid deflection errors and undesirable reduction in image brightness.

The invention has for an object to keep the voltage across the load substantially constant in a simple and efficient manner, and is characterized in that a series combination of a light-radiating element, a light-sensitive resistor and the load is connected to the voltage source. The lightsensitive resistor is optically coupled to the light radiating element so as to regulate the load voltage.

The invention will be described more fully with reference to the accompanying drawing, in which FIG. 1 shows a schematic diagram of a voltage regulator according to the invention;

FIG. 2 is a diagram useful in explaining the operation of a voltage regulator according to the invention;

FIG. 3 illustrates another embodiment of the invention; and

FIG. 4 illustrates the details of the mask arrangement of the arrangement shown in FIG. 3.

A voltage source U having a high internal resistance 12 is to be connected to a load 50. The voltage source U may comprise, for example, the high-voltage generator of a television receiver having an of, for example, 15 kv. and an internal resistance of, for example, 1 mohm.

In accordance with the invention, the series combination of a light-sensitive resistor 4, a light radiating element 3 and the load 50 is connected to the voltage source U. The light radiating element may be a gas discharge tube, for example, a neon tube which is arranged to illuminate the photosensitive resistor 4.

If the current I through the load 50, for example, the display tube of a television receiver, varies, the current across the gas discharge tube also varies, which current is equal to the current passing through the display tube. As a consequence, the quantity of light emitted by the gas discharge tube 3 varies. This light is received by the light-sensitive resistor 4. As a result, the resistance value of the light-sensitive resistor 4 is changed. The resistance value decreases when the current I, and hence the quantity of emitted light, increases.

With an increasing current I, the voltage drop across the internal resistance 12 of the generator also increases. By a suitable choice of the light-sensitive resistor and/or of the light radiating element, it can be ensured that the increase in voltage drop across the internal resistance 12 is compensated substantially by the reduction in voltage drop across the light-sensitive resistor 4. It will be obvious that all other variable sources of light must be prevented from striking light-sensitive resistor 4 so that resistor 4 may respond exclusively to variations in light produced by the load variations.

In order to obtain the desired compensation, there may be arranged, as an alternative, a mask of suitable size on the light source and/or on the light-sensitive resistor. It is then necessary that the magnitude of the light spot produced by the light source be a function of the current passing through the light source.

If at least one dimension of the light spot produced by the source of light shifts as a function of the current passing through the light source, it can be ensured by a special shape of the sides of the mask, in addition to the variation in brightness, that the light from the light source 3 striking the light-sensitive resistor 4 varies in the desired manner as a function of the current flowing. The light controls the resistance value of the branch including the elements 12, 3 and 4 in a manner such that the output voltage at the load resistor 50 remains at least substantially constant. The design should preferably be such that the resistance variation of the resistor 4 with respect to the overall resistance of the elements 12, 3 and 4 has the same value as the variation of the current I with respect to the total current, or the resistance variation of the resistor 50 with respect to the value of this resistor.

FIG. 3 illustrates an arrangement using the combination of a glow discharge tube in which the length of the glow discharge varies with the current and a triangular mask. The circuit of FIG. 3 is similar to the circuit shown in FIG. 1 and includes a source of voltage U of high internal impedance 12. Connected in series therewith are a glow discharge tube 3, a photosensitive resistor 4, and the load 50 to be regulated. The length of the glow produced by electrode 20 is a function of the current flow in the series circuit. A light shield 22 having an aperture therein surrounds tube 3. The photosensitive resistor 4 is positioned opposite the shield aperture. A triangular mask 25 is interposed between the tube 3 and the photosensitive resistor 4. FIG. 4 illustrates the arrangement of mask, photosensitive resistor and glow electrode in greater detail. The system of FIG. 3 regulates the load voltage in the manner described above.

Experiments were performed in which the masks were papers of aquadag aflixed to the light source. In particular, the masks were affixed to the cylindrical bulb of a neon glow discharge tube of the type disclosed in US. Patent 2,733,372. As is known, the length of the glow discharge in such a tube is substantially proportional to the current strength through the tube.

In one embodiment, the E.M.F. of the voltage source U was 500 volts and the internal resistance of the source was k9. The light source 3 was a neon tube type 4662 and the light-sensitive resistor 4 was a CdS cell type ORP 32. r

The measured voltage V across the variable load 50 is illustrated in FIG. 2 as a function of the current I for three different shapes of the mask on the neon tube. The papers of aquadag had a triangular shape, the height of which was about 3 cms. The base of the triangle was given three diiferent values.

It is also possible to connect a resistor in parallel with the light-sensitive resistor 4 thereby to reduce the slope of the characteristic curve approximately to zero for currents of less than 0.3 ma.

Instead of a gas discharge tube, use may be made of a pn-recombination radiation source, i.e. a light radiating diode driven in the forward direction.

It may often be desirable to cause a finite current to pass through the radiation source even in the absence of a current through the load 50, in this case in the absence of a current through the display tube of the television receiver. To accomplish this result, a fixed resistor may be connected in parallel with the variable load 50. In this way the voltage across the display tube is prevented from rising to an excessively high value in the absence of any current flow therein.

It is useful to have a low voltage supplied to the lightsensitive element 3. In FIG. 1, the light sensitive element 3 then should be connected between the terminal 1 and the lower side of the load resistor 50.

In the case of rapid variations it is desirable to connect a capacitor in parallel With the light-sensitive resistor or with the series combination of the light-sensitive resistor and the light radiating element. Although the invention has been described in connection with a specific embodiment, many modifications thereof will be apparent to those skilled in the art without departing from the inventive concept, the scope of which is set forth in the appended claims.

What is claimed is:

1. A circuit for regulating load voltage comprising, input terminals connected to a voltage source having a high internal impedance, a variable electrical load to be supplied from said voltage source, a light-radiating element, a photosensitive resistor, and means connecting said load, said light-radiating element and said photosensitive resistor in series circuit across said input terminals, said photosensitive resistor being positioned to receive light exclusively from said light-radiating element and being responsive thereto so that a given variation in the load impedance produces a change in the current flowing in said series circuit which causes the intensity of light received by said photosensitive resistor to vary in a sense and in an amount sufiicient to vary the resistance thereof to maintain the voltage across said load substantially constant.

2. A stabilizing circuit-arrangement as claimed in claim 1 further comprising a mask which is arranged between the light radiating element and the light-sensitive resistor and in that the size of the light spot produced by the light radiating element is a function of the current passing through said element.

3. A stabilizing circuit-arrangement as claimed in claim 1 further comprising a mask which, is aflixed to the light radiating element, and wherein said light-radiating element is a glow discharge tube having the characteristic that the length of the glow discharge is substantially proportional to the current passing through the tube.

4. A stabilizing circuit-arrangement as claimed in claim 3, characterized in that the mask is aihxed to the cylindrical bulb of the glow discharge tube, the mask having 'a triangular shape.

5. A circuit as described in claim 1 wherein the intensity of the light produced by said light-radiating element is a function of the current flow therein and varies in the same sense as said current and wherein said photosensitive resistor has the characteristic of a decrease in resistance with an increase of illumination.

6. A circuit as described in claim 5 wherein said lightradiating element is a gas discharge tube and further cornprising 'a resistor connected in parallel with said photosensitive resistor.

7. A circuit as described in claim 5 further comprising a capacitor connected across the series combination of said photo-sensitive resistor and said light-radiating element.

8. A circuit for regulating load voltage comprising, input terminals connected to a voltage source having a high internal impedance, a variable electrical load to be supplied from said voltage source, a light source, a photosensitive resistor having the characteristic of a decrease in resistance with an increase of illumination, means connecting said load, said light source and said photosensitive resistor in series circuit across said input terminals, and means for optically coupling said photo-sensitive resistor exclusively with said light source so that the light striking said photosensitive resistor varies as a function of the current in said series circuit to produce a variation in the resistance of the photosensitive resistor with respect to the overall impedance composed of said source internal impedance, said photosensitive resistor and said light source, which is equal to the variation of impedance of said load with respect to the impedance value of said load.

9. A circuit for regulating load voltage comprising, input terminals connected to a voltage source having a high internal impedance, a variable electrical load to be supplied from said voltage source, a light source, a photosensitive resistor, means connecting said load, said light source and said photosensitive resistor in series circuit across said input terminals, said photosensitive resistor being positioned to receive light exclusively from said light source and being responsive thereto to produce a change in resistance sufficient to maintain the voltage across said load substantially constant.

10. A circuit as described in claim 9 further comprising a capacitor connected in parallel with said photosensitive resistor and a resistor connected in parallel with said load.

11. A circuit as described in claim 9 arranged so that the intensity of light striking said photosensitive resistor is a function of the current in said series circuit and wherein the elements of said series circuit are chosen so that for a given percentage change of the load impedance, the resistance of said photosensitive resistor changes by an amount such that the total impedance of said series circuit, including the source impedance, exhibits a percentage change in impedance equal to that of the load.

12. A circuit as described in claim 9 wherein said light source comprises a gas discharge tube having a given value of breakdown voltage, and wherein the voltage amplitude of said voltage source is greater than said given value of voltage.

References Cited by the Examiner UNITED STATES PATENTS 2,573,373 10/1951 Wales 250--217 X 2,904,695 9/1959 White 250206 2,997,630 8/1961 Kruse 250205 3,040,241 6/1962 Wunderman 32366 RALPH G. NILSON, Primary Examiner.

J. D. WALL, Assistant Examiner. 

1. A CIRCUIT FOR REGULATING LOAD VOLTAGE COMPRISING, INPUT TERMINALS CONNECTED TO A VOLTAGE SOURCE HAVING A HIGH INTERNAL IMPEDANCE, A VARIABLE ELECTRICAL LOAD TO BE SUPPLIED FROM SAID VOLTAGE SOURCE, A LIGHT-RADIATING ELEMENT, A PHOTOSENSITIVE RESISTOR, AND MEANS CONNECTING SAID LOAD, SAID LIGHT-RADIATING ELEMENT AND SAID PHOTOSENSITIVE RESISTOR IN SERIES CIRCUIT ACROSS SAID INPUT TERMINALS, SAID PHOTOSENSITIVE RESISTOR BEING POSITIONED TO RECEIVE LIGHT EXCLUSIVELY FROM SAID LIGHT-RADIATING ELEMENT AND BEING RESPONSIVE THERETO SO THAT A GIVEN VARIATION IN THE LOAD IMPEDANCE PRODUCES A CHANGE IN THE CURRENT FLOWING IN SAID SERIES CIRCUIT WHICH CAUSES THE INTENSITY OF LIGHT RECEIVED BY SAID PHOTOSENSITIVE RESISTOR TO VARY IN A SENSE AND IN AN AMOUNT SUFFICIENT TO VARY THE RESISTANCE THEREOF TO MAINTAIN THE VOLTAGE ACROSS SAID LOAD SUBSTANTIALLY CONSTANT. 